In these years, a bipolar transistor with a polysilicon film used for an emitter electrode is often used in a communication device or the like, for which high speed and high integration are demanded. The structure of the bipolar transistor and the manufacturing method thereof are disclosed in PLT 1, for example.
In addition, the electric current amplification rate β (alternatively, referred to as hFE) is given as a representative characteristic of the bipolar transistor. In general, β is a parameter that fluctuates very easily. As to a reduction in the variation of β (that is, β variation), various studies have been made. For example, PLT 2 discloses a method of reducing the β variations resulting from variations in a natural oxide film thickness, by implanting fluorine (F) ions into a polysilicon film to be an emitter electrode, and further performing heat treatment, so as to break up the natural oxide film existent at a boundary between the polysilicon film and the base layer and to reduce a positive hole reverse injection barrier.